1. Field of the Invention
The present invention relates to compositions comprising a polyolefin (A), a saponified product of an ethylene-vinyl acetate copolymer (B) and an inorganic material (C.sub.1) such as titanium dioxide, being free from troubles at melt formation caused by insufficient compatibility, such as charred resin on screw, generation of gelled matter, pressure increase in extruder and flow instability. The present invention also relates to compositions comprising the above (A) and (B) and at least one member selected from the group consisting of a compound such as hydrotalcite (C.sub.2) and a polyolefin modified with an unsaturated carboxylic acid or derivatives thereof (C.sub.3), being free from generation of unordinary molding, i.e. generation of turbulence (wavy pattern) on molded articles, caused by insufficient compatibility.
2. Description of the Prior Art
Blend compositions comprising a polyolefin, an EVOH and an inorganic material such as titanium dioxide have distinctive properties. In particular, it is known that the use of the above compositions instead ofpolyolefin in multilayered co-extrusion of EVOH with various polyolefins provides molded articles with distinctive appearances, such as paper-like and high-grade feeling with what is known as "pearl luster". See for example Japanese Patent Application Laid-open Nos. 142650/1980 and 154232/1980. However, these compositions are generally poor in compatibility within themselves and, hence, when formed into film, sheet, bottle or the like by extrusion molding, tend to generate nonuniform phase-separated irregular matters. The number of the irregular matters increases particularly upon long-period operation to significantly impair the appearance of the molded articles. Where titanium dioxide, in particular, is used as the inorganic material, there occurs many troubles including generation of black deposit ("charred resin on screw") in the extruder, that of gelled matters ("lip stain") sticking to the dielip, and the like, thereby markedly deteriorating the appearance and mechanical properties of molded articles. The composition proposed by Japanese Patent Application Laid-open No. 199040/1985 (U.S. Pat. No. 4,613,644) is effective to eliminate the above troubles when the content of EVOH is small but does not completely eliminate them when the amount of EVOH becomes larger. Where talc is used as the inorganic material, flow instability occurs immediately after the starting of molding operation, then gelled matters accumulate on the dielip and other parts to impair the appearance of molded articles, and further the inside pressure of the extruder increases to render it impossible to continue the operation. Extrusion molding of the composition comprising polyolefin, EVOH and an inorganic material thus has not been practiced, or, has, if ever, been practiced only for a short time period, in spite of the fact that the molded articles showed excellent characteristics.
There has been proposed, for the purpose of improving gas barrier properties of polyolefin, blending polyolefin with EVOH having high gas barrier property. See for example Japanese Patent Application Laid-open No. 38984/1974 (U.S. Pat. No. 3,931,449). However, in this process, the blending ratio of polyolefin must be at least 50 parts by weight based on the total weight to secure an adhesion between polyolefin and said blend, and, then, the blend causes flow instability to occur upon molding due to poor compatibility between the polyolefin and EVOH within the blend, thereby yielding poor appearance of molded articles. Further Japanese Patent Application Laid-open No. 39380/1978 proposes that 25 to 60 parts of an EVOH having a melt index of at least 3 times that of the polyolefin to be blended and 5 to 40 parts of a saponified product of an ethylene-vinyl acetate copolymer having an ethylene content of 70 to 98 mol % and a saponification degree of vinyl acetate component of at least 20% are added to 100 parts of polyolefin and the obtained blend is laminated with polyolefin. However, it does not disclose that flow instability such as lip stain on dielip, which generates when talc, etc. is blended, can be prevented thereby. Furthermore, the compatibility of the saponified product of ethylene-vinyl acetate copolymer with polyolefin is still poor, thereby causing intralayer delamination and lowering the strength of the molded articles. When this blend is used as an outer layer, molded articles have pear-skin pattern and turbulence (wavy pattern) on their surface and cannot be used for practical purposes.
Japanese Patent Application Laid-open No. 199040/1985 (U.S. Pat. No. 4,613,644) discloses a resin composition comprising polyolefin (A), EVOH (B) and a compound such as hydrotalcite (C.sub.2) to prevent charred resin on screw in molding operation. This resin composition however has, upon melt molding or co-extrusion molding, for example when the EVOH is used in a large amount, problem of generating wavy pattern on the surface of molded articles.